Objective: To determine the prevalence of cytomegalovirus (CMV) isolates resistant to ganciclovir sodium or foscarnet sodium at the time of diagnosis of CMV retinitis, prior to the initiation of therapy.
Design: Prospective epidemiologic study.
Setting: An acquired immunodeficiency syndrome ophthalmology clinic.
Patients: Patients with acquired immunodeficiency syndrome and newly diagnosed CMV retinitis.
Intervention: Culturing blood and urine samples for CMV and testing of all positive isolates for sensitivity to ganciclovir and foscarnet.
Main outcome measure: Prevalence of the following: blood culture isolates resistant to ganciclovir (inhibitory concentration 50% [IC50] > 5.5 mumol/L) or foscarnet (IC50 > 400 mumol/L) and urine culture isolates resistant to ganciclovir or foscarnet.
Results: Forty-nine patients were enrolled during a 13-month period. Forty-four patients had blood culture samples that could be evaluated; of these, 66% were positive (59% of patients). Thirty-four patients had urine cultures that were evaluable; of these, 82% were positive (57% of patients). Overall, 78% of patients had either a urine or blood culture sample positive for CMV. No blood culture isolates were resistant to ganciclovir, and only 1 urine culture isolate (2% of patients) was resistant to ganciclovir. Three percent of blood culture isolates and 4% of urine culture isolates (2% and 2% of patients, respectively) were resistant to foscarnet. Overall, 4% of patients had either a blood or urine culture isolate resistant to foscarnet.
Conclusion: Resistance to ganciclovir or foscarnet at the time of diagnosis of CMV retinitis is uncommon.